In bulk polymerization techniques for the preparation of carboxyalkylpolysiloxanes, it is not uncommon to react a vinyl functional siloxane with thioglycolic acid HSCH.sub.2 COOH, which reaction provides a sulfur containing carboxy functional polymer. However, the sulfur odor inherent in such materials precludes their widespread use. In contrast, and according to the present invention, a sulfur-free route to carboxyalkylpolysiloxanes is provided.
In emulsion and microemulsion polymerization techniques for the preparation of carboxyalkylpolysiloxanes, it is also not uncommon to employ a carboxyalkyl trialkoxysilane as one of the precursors in order to impart functionality to the siloxane polymer. However, carboxyalkyl trialkoxysilanes typically have a considerable solubility in water, and therefore only partially incorporate into the siloxane polymer droplets formed during the ring opening polymerization reaction. As a consequence, one can only expect a low level of the carboxyalkyl trialkoxysilane to become incorporated into the siloxane polymer. In addition, the carboxyalkyl trialkoxysilane generates a significant amount of alcohol as a by-product, most commonly methanol, according to the reaction: EQU RSi(OCH.sub.3).sub.3 +3H.sub.2 O.fwdarw.RSi(OH).sub.3 +3CH.sub.3 OH.
While methanol is not classified as carcinogenic, it can be acutely toxic if ingested, and may even be fatal or result in blindness. Methanol is a general irritant to the skin and mucous membranes, and prolonged skin contact with methanol vapor or liquid can cause dermatitis. Therefore, it would be advantageous in applications especially in the personal care arena, to eliminate its presence.
In contrast, and according to the present invention, one can expect that the extent of incorporation of carboxy functionality into the siloxane polymer will improve with the use of the dialkyl, alkyl carboxyalkyl cocyclic siloxane due to its increased nonpolarity and hence its decreased water solubility. In addition, the dialkyl, alkyl carboxyalkyl cocyclic siloxane liberates no by-product of any kind.
Lastly, carboxyfunctional siloxanes are useful in the treatment of substrates such as hair and textiles, due to their siloxane lubrication properties, and durability imparted by the carboxy group. However, odor issues, i.e., sulfur containing, and poor process economics have generally hindered their widespread use in these commercial applications. This invention improves both the odor profile and the process economics.